Removes python version from .travis.yml
Removes python version from .travis.yml

This remove specification of python version from .travis.yml.
We do not need it b/c we use travis environments and we use TOX_ENV
variable in them - and this is the place where we are overriding python
version from default travis env.

tuskar/tuskar,rdo-management/tuskar,rdo-management/tuskar,rdo-management/tuskar